The present portable electronic devices usually use the battery as the power supply device. When the battery power runs out, the electronic device needs to be charged by an adapter to ensure the normal work. With wide adaptive range and high converting efficiency, the switched-mode power supply (SMPS) has been widely applied to portable electronic devices.
The SMPS usually comprises two modes: the pulse width modulation (PWM) mode and the pulse frequency modulation (PFM) mode, which may be converted through a hybrid converter for the SMPS. And like the SMPS, the hybrid converter for the SMPS has been widely applied to portable electronic devices.
In the PWM mode, the hybrid converter for the SMPS works under a constant frequency, and a PWM controlling unit adjusts the conduction time of the power switch according to the load situation. In the PFM mode, the hybrid converter for the SMPS usually has a strong load capacity and may output an output voltage with small ripple and constant frequency. In a heavy load condition, a high efficiency may be achieved; but in a light load condition, the constant switching loss of the hybrid converter for the SMPS may decrease the efficiency.
In the PWM mode, the frequency of the hybrid converter changes according to the value of the load. In a light load condition, the frequency decreases and causes a corresponding decrease in the switching loss, which may result in the hybrid converter achieving a high efficiency under the light load.
As mentioned above, when in which the hybrid converter automatically switches between PWM and PFM modes according to the load condition, the hybrid converter may maintain a high efficiency, which may enable the power supply to achieve high efficiency and the battery to achieve longer endurance. Conventionally, a hybrid converter that can automatically switch between two modes requires an automatic conversion controlling circuit, a PWM circuit and a PFM circuit. The automatic conversion controlling circuit controls the PWM circuit and the PFM circuit to work according to the load condition so as to make the main circuit of the power supply output a stable voltage. However, the automatic conversion controlling circuit is complicated and hard to realize.